The invention concerns a theft protection device for motor vehicles. In order to counter a rising number of motor vehicle thefts, stop-drive devices are used increasingly especially in new vehicles. The operation of said devices is based on releasing the functions of at least one motor control device that is essential for the vehicle operation only if a code that is entered from the outside into the stop-drive device coincides with a code previously stored inside the stop-drive device. Devices of this type ensure a high degree of safety against attempted thefts, provided the secured vehicle is parked and the potential thief is not in possession of the regular means for starting. However, there has been a tendency in recent times to steal vehicles not through irregular starting, but through so-called xe2x80x9ccar-jacking.xe2x80x9d In that case, a thief forces the vehicle user to hand over the regular starting means and then has unlimited access to the vehicle. A device for safeguarding a vehicle, which at least makes car-jacking more difficult, is known from the U.S. Pat. No. 4,302,747. A vehicle secured in accordance with the suggestion in this reference is shut down following a predetermined time interval that begins with the starting of the engine, provided a hidden switch to prevent this is not activated. However, even this known device loses its protective effect, in particular for a car-jacking, if a thief proceeds on the assumption that such a switch existsxe2x80x94which will usually be the case when such protective devices are more widely usedxe2x80x94and orders the user to provide a complete explanation of all safety devices. A safety device using the option of wireless communication between a vehicle and a locally fixed monitoring station is known from the DE-OS 42 43 482. In this case, a check is made with the aid of signals exchanged between a locally fixed monitoring station and the secured vehicle to determine whether an authorization-check communication occurs as required within the vehicle between a transmitting device on the vehicle and a transmitting device integrated into the ignition key that is handled by the user. If an error occurs in the authorization-check communication, in particular if it does not occur at all because the vehicle was short-circuited, then this is detected in the locally fixed monitoring station. The stolen vehicle can be located with the aid of identification data transmitted to the monitoring station without the knowledge of the illegal user. This arrangement as well is useless in cases where the thief has taken possession of the regular starting means, in this case the ignition key.
It is the object of the invention to provide a safety device for vehicles, which prevents the illegal takeover of a vehicle even in cases where a potential thief has taken possession of the standard starting means.
Vehicles equipped according to the invention require the regular renewal of the release for operation by feeding in a release information, generated by locally fixed code takeover/output stations. By blocking the output of this release information, the further operation of a vehicle can be prevented easily. The release information functions like a necessary operating means, which is no longer supplied in case of an illegal start-up. This makes the theft of a vehicle unappealing, even if the thief is in possession of the correct starting means and has knowledge of the design of the safety device.
In an advantageous embodiment, the release information that is necessary for further operation is supplied with the aid of a chip card of the type like a credit or telephone card. Code acquisition devices on the vehicle or locally fixed code takeover/output stations are correspondingly designed as card reading or card reading/recording devices. It is particularly advantageous if the locally fixed card reading/recording stations are erected at gasoline stations. The release information on the chip card is renewed each time during the fueling.
Another advantageous embodiment provides that the code acquisition device on the vehicle is designed as a receiving device for the radio signals and the locally fixed code takeover/output device as a radio signal transmitter/receiver. The regular renewal of the release information occurs via wireless in this case. For a sensible modification of this embodiment, the code acquisition device is also suited for emitting signals, by means of which it requests the release information in each case.
In a simple way, the operating time or the distance are applied as a vehicle use parameter for determining the driving range that is respectively valid following the input of a release information.
In accordance with another advantageous embodiment, the respective vehicle position is acquired as a vehicle use parameter, and the acquired position is compared to a driving range that was previously defined as release information.
If the release information does not arrive, it is further advisable to shut down the vehicle gradually upon leaving the driving range, for example by initially limiting the maximum speed.